In general, devices such as printers connected to networks can be used from client personal computers (PCs) over the networks. A client PC first finds a device on a network and then installs therein driver software for using the found device. Several techniques for searching for a device on a network have been available. In some techniques, search request packets are sent via broadcast or multicast. Broadcast and multicast are methods by which data is sent to a plurality of devices present in a network. In those techniques, a client PC sends a search request packet via broadcast or multicast, and a device that receives the search request packet sends a search response packet to the client PC. Thus, the device is found.
Further, a large scale network can be constructed by connecting networks to each other via connection devices such as routers. In such a network, broadcast or multicast routing may affect the traffic of the overall network and routers are generally operated so that such routing is avoided. Segmented networks created by routers are referred to as subnetworks or subnets and broadcast and multicast routing are generally available within a subnet. In such an environment, broadcast- or multicast-based network device search technology prevents a search request packet sent from a client PC from passing through a router. In a network environment where a plurality of subnets are connected via routers, therefore, it is difficult for a client PC to find a device present in a different subnet.
Accordingly, search systems that allow search for a device in a subnet using a client PC in another subnet have been developed. In an example of such search systems, a search server (discovery proxy (DP)) is located on a network. A client PC sends a search request message including a search condition to a DP, and the DP searches for a device on behalf of the client PC in response to the search request message (see, for example, Patent Citation 1).
The search system of the related art described above allows a client PC to search for all devices present in a subnet different from that in which the client PC is present. In practice, however, usage differs from one device to another. For example, some devices are permitted to be accessed from a client PC within the same subnet and other devices are permitted to be accessed from outside the same subnet. For instance, in an intranet where a subnet is provided for each section, a device can be accessed only from a specific section and another device can be accessed from all the sections. With the use of the method of the related art described above, however, all devices may be accessible (or searchable) from outside subnets regardless of such a situation.    Patent Citation 1: Japanese Patent Laid-Open No. 2001-216107